This collection of articles has been compiled on the occasion of Klaus Schredelseker's 65th birthday. The papers in this volume have been contributed both by (former) colleagues here at the University of Innsbruck and by international researchers in the field. The general topic, viz., the interplay of information, interaction of market participants, and market efficiency, has been selected because it has been the focus of Klaus' research interests for many years. Questions in this area, such as the usefulness of financial information for making investment decisions, are analyzed using a variety of methods, leading to interesting new insights.